# Referensi Cepat systemd

*Manajemen layanan, unit, timer, dan journalctl*

> Source: systemd Documentation (systemd.io) · MIT

## Manajemen Layanan

### Perintah Layanan Dasar

```
systemctl start nginx
systemctl stop nginx
systemctl restart nginx
systemctl reload nginx    # reload config
systemctl status nginx
```

### Enable / Disable

```
systemctl enable nginx    # start at boot
systemctl disable nginx   # remove from boot
systemctl enable --now nginx  # enable + start
systemctl is-enabled nginx
```

### Status Layanan

| Command | Description |
|---------|-------------|
| `active (running)` | Layanan berjalan normal |
| `active (exited)` | Berjalan sekali dan selesai dengan sukses |
| `inactive (dead)` | Layanan dihentikan |
| `failed` | Layanan crash atau keluar dengan error |
| `activating` | Layanan sedang dijalankan |

## File Unit

### Lokasi File Unit

| Command | Description |
|---------|-------------|
| `/etc/systemd/system/` | Unit buatan admin (prioritas tertinggi) |
| `/run/systemd/system/` | Unit yang dibuat saat runtime |
| `/usr/lib/systemd/system/` | Unit yang diinstal paket |
| `~/.config/systemd/user/` | Unit tingkat pengguna |

### Unit Layanan Dasar

```
[Unit]
Description=My Application
After=network.target
[Service]
ExecStart=/usr/bin/myapp --config /etc/myapp.conf
Restart=on-failure
User=appuser
[Install]
WantedBy=multi-user.target
```

### Terapkan Perubahan

```
systemctl daemon-reload   # reload unit files
systemctl restart myapp   # apply changes
```

## Timer

### Unit Timer

```
[Unit]
Description=Run backup daily
[Timer]
OnCalendar=*-*-* 02:00:00
Persistent=true
[Install]
WantedBy=timers.target
```

### Sintaks OnCalendar

| Command | Description |
|---------|-------------|
| `*-*-* 02:00:00` | Setiap hari pukul 02:00 |
| `Mon *-*-* 09:00:00` | Setiap Senin pukul 09:00 |
| `*-*-01 00:00:00` | Hari pertama setiap bulan |
| `hourly / daily / weekly` | Jadwal singkat |

### Manajemen Timer

```
systemctl list-timers --all
systemctl start backup.timer
systemctl enable backup.timer
systemd-analyze calendar "daily"
```

## Target

### Target Umum

| Command | Description |
|---------|-------------|
| `multi-user.target` | Boot normal, multi-pengguna, tanpa GUI |
| `graphical.target` | Desktop GUI lengkap |
| `rescue.target` | Mode rescue single-user |
| `emergency.target` | Shell minimal, hanya root |
| `network-online.target` | Jaringan sudah terkonfigurasi penuh |
| `timers.target` | Semua unit timer siap |

### Perintah Target

```
systemctl get-default
systemctl set-default multi-user.target
systemctl isolate rescue.target
systemctl list-dependencies graphical.target
```

## Journalctl

### Melihat Log

```
journalctl -u nginx        # logs for unit
journalctl -u nginx -f     # follow (tail)
journalctl -u nginx --no-pager
journalctl -b              # current boot only
```

### Filter Log

```
journalctl --since "2026-03-01"
journalctl --since "1 hour ago"
journalctl -p err          # errors and above
journalctl _PID=1234
```

### Level Prioritas

| Command | Description |
|---------|-------------|
| `emerg (0)` | Sistem tidak dapat digunakan |
| `alert (1)` | Tindakan segera diperlukan |
| `crit (2)` | Kondisi kritis |
| `err (3)` | Kondisi error |
| `warning (4)` | Kondisi peringatan |
| `info (6)` | Informasional |
| `debug (7)` | Pesan level debug |

### Pemeliharaan Log

```
journalctl --disk-usage
journalctl --vacuum-size=500M
journalctl --vacuum-time=30d
```

## Jaringan

### networkctl

```
networkctl list
networkctl status eth0
networkctl up eth0
networkctl down eth0
```

### systemd-resolve

```
resolvectl status
resolvectl query example.com
resolvectl flush-caches
resolvectl statistics
```

### Tunggu Jaringan

```
# In unit file [Unit] section:
After=network-online.target
Wants=network-online.target
```

## Mount

### Unit Mount

```
[Unit]
Description=Mount data volume
[Mount]
What=/dev/sdb1
Where=/mnt/data
Type=ext4
Options=defaults,noatime
[Install]
WantedBy=multi-user.target
```

### Unit Automount

```
[Unit]
Description=Automount data on access
[Automount]
Where=/mnt/data
TimeoutIdleSec=300
[Install]
WantedBy=multi-user.target
```

### Konvensi Penamaan

| Command | Description |
|---------|-------------|
| `/mnt/data` | File unit: `mnt-data.mount` |
| `/var/lib/app` | File unit: `var-lib-app.mount` |

*Path mount dengan `/` diganti `-`, tanda hubung awal dihilangkan*

## Environment

### Mengatur Variabel Environment

```
[Service]
Environment=APP_ENV=production
Environment=PORT=8080
EnvironmentFile=/etc/myapp/env
```

### Format File Environment

```
# /etc/myapp/env
APP_ENV=production
DATABASE_URL=postgres://localhost/db
SECRET_KEY=changeme
```

### Hardening Layanan

| Command | Description |
|---------|-------------|
| `ProtectSystem=strict` | Filesystem hanya-baca kecuali path yang diizinkan |
| `ProtectHome=true` | Sembunyikan /home, /root, /run/user |
| `NoNewPrivileges=true` | Cegah eskalasi hak istimewa |
| `PrivateTmp=true` | /tmp terisolasi untuk layanan |
| `ReadWritePaths=/var/lib/myapp` | Izinkan penulisan ke path tertentu |

## Dependensi

### Direktif Urutan dan Ketergantungan

| Command | Description |
|---------|-------------|
| `After=b.service` | Mulai setelah b (hanya urutan) |
| `Before=b.service` | Mulai sebelum b (hanya urutan) |
| `Requires=b.service` | Dependensi keras; gagal jika b gagal |
| `Wants=b.service` | Dependensi lunak; tidak gagal jika b gagal |
| `BindsTo=b.service` | Berhenti ketika b berhenti |
| `Conflicts=b.service` | Tidak bisa berjalan bersamaan dengan b |

### Inspeksi Dependensi

```
systemctl list-dependencies nginx
systemctl list-dependencies --reverse nginx
systemd-analyze dot nginx.service | dot -Tsvg > deps.svg
```

## Pola Umum

### Kebijakan Restart

| Command | Description |
|---------|-------------|
| `Restart=no` | Tidak pernah restart (default) |
| `Restart=on-failure` | Restart jika keluar dengan kode non-nol |
| `Restart=always` | Selalu restart (untuk daemon) |
| `RestartSec=5` | Tunggu 5 detik sebelum restart |
| `StartLimitBurst=3` | Maksimum restart dalam interval |
| `StartLimitIntervalSec=60` | Interval untuk penghitungan burst |

### Override Tanpa Mengedit

```
systemctl edit nginx  # creates drop-in
# /etc/systemd/system/nginx.service.d/override.conf
systemctl cat nginx   # show effective config
systemctl revert nginx  # remove overrides
```

### Analisis Sistem

```
systemd-analyze                  # boot time
systemd-analyze blame            # per-unit time
systemd-analyze critical-chain
systemctl list-units --failed
```